1. Field of the Invention
The present invention relates to an ink jet recording head that jets ink droplets on a record medium to form an image, an ink jet recording device and a head manufacturing method.
2. Description of the Related Art
Recently, an ink jet recording device is drawing attention as a low-cost quality color recording device. For an ink jet recording head of an ink jet recording device, there are known a piezoelectric type ink jet recording head that jets ink from a nozzle by pressure generated by mechanically deforming a pressure chamber by a piezoelectric material for example and a thermal ink jet recording head that energizes a heater element arranged in an individual passage and jets ink from a nozzle by pressure acquired by vaporizing ink.
For a current thermal ink jet recording head, there is known an ink jet recording head disclosed in Japanese Published Unexamined Patent Application No. Hei 9-226142 (hereinafter called a conventional example 1), Japanese Published Unexamined Patent Application No. Hei 10-76650 (hereinafter called a conventional example 2), Japanese Published Unexamined Patent Application No. Hei 9-327921 (hereinafter called a conventional example 3) and others.
Referring to FIGS. 20 to 23, an ink jet recording head in the conventional example 1 will be described below. FIG. 20 is a perspective view showing an example of the ink jet recording head and an ink supply part respectively mounted in a conventional type ink jet recording device and FIG. 21 is a sectional view viewed along the line Bxe2x80x94B in FIG. 20.
As shown in FIGS. 20 and 21, plural individual passages 102 are formed in a head chip 100 and a nozzle 104 for jetting ink is formed at the end of each individual passage. The plural individual passages 102 communicate with a common liquid chamber 106 inside. Each heater element 108 is provided on the plural individual passages 102, ink in the individual passage 102 foams by heat generated by the heater element 108 and recording is performed by jetting ink from the nozzle 104 by pressure acquired by foaming. Also, the common liquid chamber 106 is provided with a communicating port 110 for supplying ink from the outside.
An ink supply member 112 is arranged on the upside of the head chip 100. The ink supply member 112 is provided with an ink passage pipe 114 for supplying ink supplied from an ink tank not shown to the head chip 100. A filter may be inserted between the ink tank and the ink passage pipe 114 to filter minute solid matters in ink so that they are prevented from entering the head chip 100 to prevent blocking of a nozzle.
The head chip 100 is formed by bonding a passage substrate 120 where the individual passage 102, the common liquid chamber 106 and others are formed and a heater element substrate 126 where the heater element 108, a signal processing circuit 122 for driving the heater element 108 and a driver circuit 124 are formed as shown in FIG. 22.
Referring to FIG. 22, a method of producing the head chip 100 made up as described above will be described below.
For a method of producing the heater element substrate 126, technology for manufacturing LSI and its production facilities for example can be used. A heat storage layer, an exothermic layer to be the heater element, a protective layer for preventing the heater element from being broken by the pressure of bubbles generated by the heat of the heater element and others are laminated on a monocrystalline silicon wafer 128 as shown in FIG. 22A. Further, for a protective layer to protect from ink, a resin layer 130 made of photosensitive polyimide for example is laminated as shown in FIG. 22B.
In the meantime, for the passage substrate 120, grooves to be the common liquid chamber 106 and the individual passages 102 and others can be formed on a silicon wafer 132 by anisotropic etching for example as shown in FIG. 22C. For a method of forming the grooves to be the common liquid chamber 106 and the individual passages 102 and others by anisotropic etching, after an etching mask is patterned on a silicon wafer which has a crystal face of  less than 100 greater than  on the surface, etching has only to be performed using the heated aqueous solution of potassium hydroxide (KOH) as disclosed in Japanese Published Unexamined Patent Application Nos. Hei 11-245413 and Hei 6-183002. The grooves to be the common liquid chamber 106 and the individual passages 102 and others formed using anisotropic etching become grooves having a desired angle as shown in FIG. 23.
Further, after two silicon wafers 128 and 132 are bonded with a resin layer 130 between them as shown in FIG. 22E after an adhesive 134 is applied on the silicon wafer 132 as shown in FIG. 22D, the two silicon wafers are diced and isolated according to a method described in Patent No. 2888474 and others and multiple head chips 100 are simultaneously manufactured as shown in FIG. 22F.
Afterward, the head chip 100 is fastened to a heat sink for outgoing radiation 136 as shown in FIGS. 20 and 21. On the heat sink 136, a printed wiring substrate 138 is also formed, power and a signal supplied from the body of the ink jet recording device are transmitted to the heater element substrate 126 via bonding wire 140 and a signal and others from various sensors provided to the heater element substrate 126 are transmitted to the body of the recording device.
The head chip 100 and the ink supply member 112 are bonded by an adhesive 142.
Ink is supplied from the ink tank to the ink jet recording head 144 manufactured as described above. Ink supplied from the ink tank flows in the ink passage pipe 114 in the ink supply member 112, enters the common liquid chamber 106 in the head chip via the communicating port (the inlet) 110 open on the upside of the passage substrate 120 of the head chip 100 and is supplied to each individual passage 102.
Next, referring to FIGS. 24 and 25, a conventional example 2 will be described. The same reference numbers are allocated to the same components for those in the conventional example 1 and a detailed description is omitted.
In the conventional example 2, an ink passage pipe 114 connecting the ink tank with a common liquid chamber 106 is integrated with a nozzle top plate 150 to which individual passages (grooves) 102 are provided. Therefore, in the conventional example 2, ink supplied to the common liquid chamber 106 via a communicating port not shown at the end of the ink passage pipe 114 also reaches the individual passage (groove) 102 and is also jetted from a nozzle 104, as in the conventional example 1.
Next, referring to FIGS. 26 and 27, the conventional example 3 will be described. The same reference numbers are allocated to the same components for those in the conventional example 1 and a detailed description is omitted.
The conventional example 3 relates to an ink jet recording head called a roof type in which ink supplied from a communicating port 110 flows in an approximately perpendicular direction along a plane 108A of a heating element 108 from a common liquid chamber 106 and is jetted from a nozzle 104 in a direction approximately perpendicular to the plane 108A as shown in FIGS. 26 and 27.
In the ink jet recording head 14 in the conventional example 1, when bubbles are left in the ink passage pipe 114 and the common liquid chamber 106, the bubbles grow while the head is used and may cause a large record defect because they block the supply of ink to each individual passage 102. Particularly, in a thermal ink jet recording head, as the temperature of ink rises due to heating of a heater element, air dissolved in the ink is deposited and the growth of a bubble in the common liquid chamber 106 is accelerated. As bubbles are grown by heat as described above, bubbles are easily grown in the common liquid chamber 106 which is in contact with a heater element substrate 126 and in a connection of the common liquid chamber 106 with an ink supply part 112.
Bubbles are not only separated by heat but enter from the ink tank with ink in supplying ink and may enter from the nozzle 104 in printing. These bubbles often concentratedly stay particularly in a region (hereinafter called a dead water region. See S in FIG. 21) where ink slightly flows in the common liquid chamber of the head chip 100. These bubbles block satisfactory printing not only in a thermal ink jet recording head but all ink jet recording heads. For example, in a piezoelectric type ink jet recording head, since even a minute bubble blocks the transmission of pressure, it often causes a significant printing defect.
The conventional examples 2 and 3 also have a problem that a dead water region S (see FIGS. 25 and 27) respectively exists in the common liquid chamber 106 and bubbles easily stay as in the conventional example 1.
As described above, for a method of exhausting bubbles staying in the dead water region S in the common liquid chamber 106, generally they are sucked from the nozzle 104. When bubbles are sucked from the nozzle 104, ink of quantity corresponding to sucked quantity is supplied from the ink tank. The supplied ink is spread along the shape of the common liquid chamber 106, is led to the individual passage 102, bubbles also proceed to the individual passage 102 together with the flow of ink and are exhausted outside from the nozzle 104 together with the ink.
However, as bubbles staying at both ends of the common liquid chamber 106 which mainly cause a defect of the quality of an image exist in a region in which the flow of ink is extremely small, it is difficult to remove them completely. Therefore, a dummy nozzle 104A apart from nozzles for printing is provided at both ends of the common liquid chamber 106 and the expulsion of bubbles at both ends has to be more effective. Also, it is also conceivable that a frequency by which the nozzle is sucked is increased, however, there is a problem that as the frequent sucking is improved, the efficiency when ink is used for printing is deteriorated and the capacity of a waste ink tank for storing sucked waste ink has to be increased to result in a large-sized device.
Further, the ink jet recording head has a problem that if continuous jetting and printing are performed, the temperature of the head rises and the stable jetting of ink is disabled. In order to avoid this state, it is necessary to monitor control that the temperature of the head, and to holt printing or reduce printing speed when the temperature exceeds a certain temperature.
The invention has been made to solve the above problems and provides an ink jet recording head wherein bubbles that cause printing failure are exhausted by a simple configuration, unnecessary consumption of ink is reduced to a minimum and stable continuous printing is enabled, an ink jet recording device and a head manufacturing method.
According to an aspect of the present invention, the ink jet recording head includes individual passages communicating with a nozzle for jetting ink droplets, a common liquid chamber communicating with each individual passage, an ink chamber for supplying ink to the common liquid chamber and a communicating passage connecting the common liquid chamber and the ink chamber. The communicating passage is formed to enable at least a bubble in size that causes a printing defect to be moved from the common liquid chamber to the ink chamber.
Of bubbles existing in the common liquid chamber, when bubbles that may cause a printing defect rise by buoyancy, they can be securely moved from the common liquid chamber to an ink tank via the communicating passage. Therefore, a printing defect can be prevented because the bubbles stay in the common liquid chamber.
According to another aspect of the present invention, the ink jet recording head includes individual passages communicating with a nozzle for jetting ink droplets, a common liquid chamber communicating with each individual passage, an ink chamber for supplying ink to the common liquid chamber and a communicating passage connecting the common liquid chamber with the ink chamber. When the jetting rate D of the ink jet recording head is Dxe2x89xa70.05, the communicating passage having a minimum width L that satisfies the following expression (2) for a bubble that satisfies the following expression (1) is formed.
{(nxc3x97Vxc3x97fxc3x97D/S)2xc3x97Cdxc3x97xcfx81xc3x97xcfx80xc3x97d2}/8 less than (xcfx81xc3x97gxc3x97xcfx80xc3x97d3)/6xe2x80x83xe2x80x83(1) 
d less than Lxe2x80x83xe2x80x83(2) 
Here, n denotes the number of nozzles, V denotes the volume of an ink droplet jetted from the ink jet recording head, f denote a maximum printing frequency, D denotes a jetting rate, S denotes the minimum cross section of the communicating passage, Cd denotes a resistance coefficient, xcfx81 denotes the density of ink, d denotes the diameter of a bubble, g denotes a gravitational constant and L denotes the minimum width of the communicating passage.
The invention proposes a bubble expulsion method different from a conventional type method and is intended to make bubbles that are generated and grow in the common liquid chamber escape into an ink tank that has no effect upon printing by the buoyancy of the bubbles themselves.
That is, in the ink jet recording head, if the minimum cross section of the communicating passage is S, the volume of an ink droplet jetted from the head is V, a maximum printing frequency is f, the number of nozzles is n, the jetting rate is D, the density of ink is xcfx81, a gravitational constant is g, a resistance coefficient is Cd, the diameter of a bubble is d and the minimum width of the communicating passage is L, then the buoyancy of a bubble d in diameter can be expressed as follows.
(xcfx81xc3x97gxc3x97xcfx80xc3x97d3)/6 
In the meantime, the maximum flow velocity of ink in the communicating passage from the ink tank to the common liquid chamber (the flow velocity of ink in a region of which the minimum cross section is S in the communicating passage) can be expressed as follows.
nxc3x97Vxc3x97fxc3x97D/S 
The resistance that acts upon a bubble according to this flow velocity can be expressed as follows.
{(nxc3x97Vxc3x97fxc3x97D/S)2xc3x97Cdxc3x97xcfx81xc3x97xcfx80xc3x97d2}/8 
That is, assuming that the average jetting rate in printing a normal text image is 5% or more, it can be said that the buoyancy of a bubble d in a diameter that satisfies the following relationship excels the resistance.
Dxe2x89xa70.05 
{(nxc3x97Vxc3x97fxc3x97D/S)2xc3x97Cdxc3x97xcfx81xc3x97xcfx80xc3x97d2}/8 less than (xcfx81xc3x97gxc3x97xcfx80xc3x97d3)/6 
Therefore, if the ink jet recording head is formed so that the minimum width L of the communicating passage satisfies the relationship d less than L between the minimum width L and the diameter d of the bubble, the bubble can be exhausted from the head (the common liquid chamber) to the ink chamber via the communicating passage.
The minimum width L of the communicating passage means the minimum one of the maximum inscribed circuits inscribed on the wall of the communicating passage at the cross section of the communicating passage.
Therefore, a bubble rising from the common liquid chamber by buoyancy can be securely moved into the ink tank. As a result, ink supply failure to the individual passage by the growth of a bubble in the common liquid chamber can be prevented and the generation of a void in a block unrecoverable of itself can be avoided. Therefore, stable ink supply is enabled and continuous printing is enabled.
As the movement of a bubble is difficult if the bubble adheres to the wall in the communicating passage, it is suitable that the following fixed margin is added (coefficient: 3).
xe2x80x83d less than L/3
If the width is set like this, bubbles can more securely pass even if they adhere to the walls on both sides. Needless to say, when a path is curved and there is a long path to go through, it is desirable that the coefficient is further increased.
According to another aspect of the present invention, the ink jet recording head includes individual passages communicating with a nozzle for jetting ink droplets, a common liquid chamber communicating with each individual passage, an ink chamber for supplying ink to the common liquid chamber and a communicating passage connecting the common liquid chamber with the ink chamber. When the jetting rate D of the ink jet recording head is Dxe2x89xa70.05, the communicating passage having the minimum cross section S that satisfies the following expression (4) for a bubble having the relationship expressed in the following expression (3) is formed.
dxe2x89xa72Npxe2x80x83xe2x80x83(3) 
{(nxc3x97Vxc3x97fxc3x97D/S)2xc3x97Cdxc3x97xcfx81xc3x97xcfx80xc3x97d2}/8 less than (xcfx81xc3x97gxc3x97xcfx80xc3x97d3)/6xe2x80x83xe2x80x83(4) 
Here, n denotes the number of nozzles, V denotes the volume of an ink droplet jetted from the ink jet recording head, f denotes a maximum printing frequency, D denotes the jetting rate, S denotes the minimum cross section of the communicating passage, Cd denotes a resistance coefficient, xcfx81 denotes the density of ink, d denotes the diameter of a bubble, g denotes a gravitational constant and Np denotes pitch between nozzles.
When a bubble of a diameter equivalent to nozzle pitch Np of two or more blocks the individual passage, no ink droplet is jetted from adjacent two or more nozzles and as a result, printing is disabled. Then, if a bubble (d greater than 2Np) the diameter of which is equivalent to pitches Np of two or more satisfies the above expression (4), the buoyancy of the bubble excels resistance and the bubble can be moved by buoyancy via the communicating passage.
Therefore, blocking adjacent plural nozzles and from causing a printing defect by a bubble is prevented by forming the communicating port having the minimum cross section S that satisfies this relationship. Therefore, an image having high reliability can be continuously formed.
According to another aspect of the present invention, the ink jet recording device includes an individual passage communicating with a nozzle for jetting ink droplets, a common liquid chamber communicating with each individual passage, an ink chamber for supplying ink to the common liquid chamber and plural communicating passages each of which connects the common liquid chamber with the ink chamber. For at least one communicating passage, an ink supply direction from the ink chamber to the common liquid chamber is set within a range of 45xc2x0 from the downside in a gravitational direction in.
If a bubble caused in the common liquid chamber rises by buoyancy when the ink supply direction from the ink chamber to the common liquid chamber is set in a range of 45xc2x0 from the downside in a gravitational direction, the bubble can be guided from the common liquid chamber to the ink chamber. Therefore, occurrences of printing failure by bubbles can be satisfactorily inhibited.